Position control for parallel hydraulic systems

ABSTRACT

A flexible rod weeder in which the weeder rods are raised and lowered by rocking the frame about the forward wheels. A plurality of gauge wheels are connected to the rear of the frame through extensible and retractable hydraulic motors so that by extending and retracting the motors, the frame is rocked about the forward wheels. The hydraulic motors are connected in parallel and are provided with an adjustable stop which will prevent the lowering of the weeder rods beyond a predetermined position, but permit the flow of fluid from one motor to another so that the gauge wheels equally share the weight of the rear of the frame.

United States Patent Inventor Edward Clyde Ryan Ankeny, Iowa Appl. No.812,577

Filed Mar. 28, 1969 Patented June 8, 1971 Assignee Deere & CompanyMoline, Ill.

POSITION CONTROL FOR PARALLEL HYDRAULIC SYSTEMS 15 Claims, 7 DrawingFigs.

[1.8. CI 91/189, 91/413, 172/44, 60/97 E, 60/52 HE Int. Cl Fl5b 13/06Field of Search 91/189, 413; 60/97 E, 52 HE [56] References Cited UNITEDSTATES PATENTS 2,622,400 12/1952 Greer .0 91/189 2,782,603 2/1957Beecroft 60/97 E Primary Examiner-Edgar W. Geoghegan Attorneys-H.Vincent Harsha, Harold M. Knoth, William A.

Murray and John M. Nolan ABSTRACT: A flexible rod weeder in which theweeder rods are raised and lowered by rocking the frame about theforward wheels. A plurality of gauge wheels are connected to the rear ofthe frame through extensible and retractable hydraulic motors so that byextending and retracting the motors, the frame is rocked about theforward wheels. The hydraulic motors are connected in parallel and areprovided with an adjustable stop which will prevent the lowering of theweeder rods beyond a predetermined position, but permit the flow offluid from one motor to another so that the gauge wheels equally sharethe weight of the rear of the frame.

PATENIEUJUM 8I87l 35 1 SHEET 1 OF 5 I INVENTOR. EDWARD CLYDE RYANPATENTEUJUM 8197i SHEET 2 BF 5 I N Vli N'I'OR. EDWARD CLYDE RYANPATENTEUJUN 8B7! SHEET 3 BF 5 FIG .6

INVIZNTOR. EDWARD CLYDE RYAN PATENTEDJUM 8l97| SHEET Q 0F 5 INVENTOR.EDWARD CLYDE RYAN PATENTEDJUH 8|97l 3583284 sum 5 0F 5 INVENTOR. EDWARDCLYDE RYAN POSITION CONTROL FOR PARALLEL HYDRAULIC SYSTEMS BACKGROUND OFTHE INVENTION The present invention relates to hydraulic systems whichhave a plurality of hydraulic motors connected in parallel, and moreparticularly relates to means for controlling the total extent ofmovement of the movable parts of a plurality of hydraulic motors whichare connected in parallel.

The embodiment of the invention disclosed herein finds great utility inconnection with the control of the raising and lowering movements ofcertain agricultural implements such as rod weeders. In the ordinarysituation, the agricultural implement such as a rod weeder is drawn by atractor and has a plurality of weeder rods adjustable vertically betweentransport and working positions by rocking the frame about a pluralityof forward wheels. A plurality of gauge wheels are connected to the rearof the frame through extensible and retractable hydraulic motors so thatby extending and retracting the motors, the frame is rocked about theforward wheels. In order that the gauge wheels equally share the weightof the rear portion of the frame, the motors are connected in parallel,and so that the motors can be actuated by the tractor operator, they arealso connected to the tractor fluid pressure system which includes thedistributing valve, a hydraulic pump and a fluid reservoir.

In the operation of a tractor-implement unit of the type describegenerally above, it is necessary for the operator to actuate the fluidpressure system at the end of each pass through a field to effectraising of the weeder rods from their groundworking positions so thatthe unit can be turned about to make an adjacent and parallel paththrough the field. It is desirable in many instances such as these thatmeans be provided to enable the operator to lower the weeder rods to thesame ground-working position as before. However, while it is well knownto provide hydraulic motors with adjustable stops to determine theextent of relative movement between the movable parts of the motor, allof the stop means heretofore known have been designed for singlecylinders or for cylinders used in series and function to lock themovable parts of the motors when the motors have been extended orretracted to the predetermined position. If the stop means of theabovedescribed type were used with the parallel connected hydraulicmotors of a rod weeder of the type generally described above,thefloating action inherent in parallel connected hydraulic motors wouldno longer be available and the gauge wheels would equally share theweight of the rear portion of the rod weeder frame only in the idealsituation where the ground surface beneath the rod weeder frame isperfectly level.

SUMMARY OF THE INVENTION The primary object of the present invention isto provide an improved hydraulic system which includes a plurality ofextensible and retractable hydraulic motors connected in parallel andlimit or control means which prevents simultaneous extension orretraction of all the motors after one of the motors has been extendedor retracted a predetermined distance, but will permit extension orretraction of less than all the motors as long as it is accompanied bysimultaneous retraction or extension respectively of one or motors.

A further objectof the present invention is to provide a hydraulicsystem having a plurality of extensible and retractable hydraulic motorsconnected in parallel and including adjustable control means whichlimits the total extent of relative movement in any given direction ofthe extensible and retractable parts of the hydraulic motors.

According to the present invention, a plurality of doubleactingextensible and retractable hydraulic motors have their anchor and rodends connected in parallel by first and second fluid lines respectively,and the first and second fluid .-line means are alternately connectablethrough third and fourth fluid line means respectively to a source offluid pressure and a fluid reservoir. A valve membermovable between openand closed positions is interposed in the third fluid line means andmoves to the open position in response to fluid pressure within thethird fluid line means when the third and fourth fluid line means areconnected to the source of fluid pressure and the reservoirrespectively. A push rod is mounted on one of the motors and isresponsive to the retraction of that motor to a predetermined positionto move the valve member to the closed position to prevent exhaust offluid through the third fluid line means. With the valve member in theclosed position, additional retraction of one or more of the motors inaccompanied by extension of one or more of the motors.

According to another feature of the invention, a yieldable means ispositioned between the extensible and retractable part of the hydraulicmotor and the push rod for moving the valve member to the closedposition so that the push rod will not prevent additional retraction ofthe motor beyond the predetermined position provided the retraction ofthat motor is accompanied by extension of one or more of the othermotors.

Other objects and important features inherent in and encompassed by theinvention will become apparent to those skilled in the art from areading of the following detailed description of the preferredembodiment of the invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a plan view of a rod weeder in which the principles of thepresent invention have been incorporated;

FIG. 2 is a sectional view taken along a line 2-2 of FIG. 1, the rodweeder being illustrated in its field transport position in full linesand in its field working position in broken lines;

FIG. 3 is a sectional view taken substantially along the line 3-3 ofFIG. 1;

FIG. 4 is a perspective view illustrating a portion of the rod weederembodying the principles of the present invention;

FIG. 5 is a perspective view illustrating a hydraulic depth controlsystem according to the present invention;

FIG. 6 is a sectional view of a valve member used in the hydraulic depthcontrol system illustrated in FIG. 5; and

FIG. 7 is a sectional view taken substantially along the line 7-7 ofFIG. 6. DESCRIPTION OF THE PREFERRED EM- BODIMENT In the followingdescription, right-hand and left-hand reference is determined bystanding at the rearof the implement and facing in the direction oftravel.

Referring now to the drawings, the illustrated rod weeder is formed of aplurality of subframes indicated generally at l0, l2 and 14. Thesubframes are supported by front ground en gaging wheels 16a, 16b, 16cand 16d and rear gauge wheels 18a, 18b, 18c and 18d. The front groundwheels 16 are fixed relative to the subframes 10, 12 and 14, and therear gauge wheels 18 are movable relative to the subframes in a mannerwhich will be more fully set forth below.

Hitch means indicated generally at 20 is secured to the forward end ofthe frame and includes right and left telescoping pole members 22 and24. Each of the hitch poles 22 and 24 include a rear hollow member 26and a forward member 28 -which can telescope within the hollow member26. The

member 26 is apertured at its forward end and carries a pin 30 which canbe disposed within a suitable aperture in member 28 to hold the pole inits desired length. The hitch poles 22 and 24 are secured to a hitchplate 32 by hitch pins 34 which pass through a clevis 36 at the forwardend of each pole and alsothrough a corresponding aperture in the hitchplate 32. The forward end of the hitch plate 32 carries clevis 38 whichis secured to a tractor drawbar 40 in any suitable manner. a Each of thesubframes includes a forward generally transversely extending framemember 42 and a rear transversely extending frame member 44. The framemembers 42 and 44 are interconnected by outer longitudinally extendingframe members 46 and intermediate longitudinally extending frame members48. The hitch poles 22 and 24 are pivotally secured to mounting beams 50(FIG. 2) depending from the frame members 46 on the center subframe.

Each of the subframes 10, 12 and 14 is provided with a rockshaft formedof rightand left-hand sections 52 and 54, respectively. Each of therockshaft sections is supported by a pair of apertured frame members 56which are secured to and extend rearwardly from the rear transverselyextending frame member 44. Each of the frame members 56 is provided witha cylindrical bearing 58 in which the rockshaft sections 52 and 54 arerotatably disposed. The two rockshaft sections 52 and 54 are joinedtogether by a boot indicated generally at 60. Each boot has right andleft upper members 62 and 64 respectively, which are joined at theirlower ends by a lower tubular member 66 in which is disposed a drivechain 68 and a sprocket 70, the weeder rod 72 passing through anaperture of the same cross section as the weeder rod in the sprocket 70.To facilitate the securement of the rockshaft sections 52 and 54 to theboot 60, the rockshaft sections are provided with facing flanges 74which are secured in any suitable manner such as bolts 76 to the uppermembers 62 and 64 of the boot. Welded or otherwise suitably secured tothe outer end of each rockshaft section 52 and 54 is an attachingbracket 78 to which a weeder rod support in the form of a gooseneckpendant 80 may be secured.

Means are provided to permit the weeder rod 72 to swing upwardly andrearwardly should an obstruction be encountered. To this end atelescoping link assembly 82 which includes a barrel member 84 and a rod86 telescopically received within the barrel member 84 has its barrelend 84 pivotally secured to a transversely extending pin 88 carriedbetween the rightand left-hand members 62 and 64 of the boot, the rod 86of the link assembly being pivotally secured to a lug 90 carried by theintermediate longitudinally extending frame member 48. A shear pin 92passes through aligned apertures in the members 84 and 86 to hold themin their extended position under normal load conditions. Should theweeder rod strike an obstruction, the pin 92 would be sheared and theweeder rod would move upwardly and rearwardly by rotating about the axisof the rockshaft sections.

Each of the weeder rods 72 is driven from the ground wheels 16 by meansof a jackshaft 94 or 96 and a drive chain 98, the drive chain 98 passingover the sprocket 100 on the jackshaft and a sprocket 102 on the boot,the sprocket 102 being concentric with a second sprocket 104 over whichthe drive chain 68 passes. The jackshaft 94 for the center section 12which cam'es two wheels 16b and 16c is interconnected with both wheelsby means of one-way ratcheting drives so that the rod weeder is turned,the jackshaft will be driven by the wheel that moves the fastest. Thejackshafts 96 which are associated with the outer subframes and 14 areof telescoping construction and have universal joints 106 which connectthem to subshafts 108 with the wheels on the center subframe 12. As inthe case with jackshaft 94, the jackshafts 96 are also driven from theright and left wheels through one-way ratcheting drive clutches.

While the drive chain 98 passes around its associated sprocket 102, thedrive chain 68 only passes over its sprocket 104, but is hold in placeby idlers 110 and 112, one of which may be adjustable to maintain theproper tension in the drive chain 68.

The gauge wheels 18 are carried by support structure indicated generallyat 114, each gauge wheel supporting structure including an arm member116 which is fixedly secured at its upper end to a C-shaped member 118which carries a bearing block 120. Each of the bearing blocks 120 isrotatably disposed about the associated rockshaft section 52 and 54 andis held in place from lateral movement by rings 121 (FIG. 4) weldedtothe rockshaft section.

The lower end of the arm 116 has a sleeve portion 122 which receives anupwardly extending spindle 124 secured to a yoke 126 which carries anaxle member 128. The upper end of the spindle is threaded and receives anut 130 which bears against a spring 132 to hold a detent block 134against the upper edge of the sleeve 122. The detent block 134 is keyedto the spindle 124 and normally holds the wheels 18 in the foreand-aftposition shown in FIG. 2, but permits it to caster when sufficientturning force is imposed upon the wheel.

The gauge wheels 18 can be moved vertically with respect to the frame torock the frames about the wheels 16 between a transport positionillustrated by the solid linesin FIG. 2 and a working positionillustrated by the dotted lines in FIG. 2. To this end, the gauge wheels18a, 18b, 18c and 18d are provided with extensible and retractabledouble-acting hydraulic cylinders 136a, 136b, 1360 and 136d. The anchorend 138 of each cylinder is secured to an upstanding lug 140 mounted onthe rear frame member 44 and the rod end 142 of each cylinder ispivotally connected by a bolt 144 to a mounting bracket 146 secured tothe arm 116.

As can best be seen in FIG. 5, the anchor ends of the cylinders 136 areinterconnected by first fluid lines 148 and the rod ends of thecylinders 136 are interconnected by second fluid lines 150. The fluidlines 148 and 150 are connected to one side of a directional flowcontrol valve 152 by fluid lines 154 and 156 respectively, while theopposite side of the directional flow control valve 152 is connected toa pump 158 and a fluid reservoir 160. The fluid lines 148 and 154provide a parallel connection between the anchor ends of the cylinders136 and the valve 152, while the fluid lines 150 and 156 provide aparallel connection between the rod ends of the cylinders 136 and thevalve 152. When the valve 152 is moved to the right as viewed in FIG. 5,fluid pressure is supplied to the anchor ends of the cylinders 136 toextend the rods to move the weeder rod 72 to the transport position.When the valve 152 is moved to the left, the rod ends of the cylinders136 are supplied with fluid pressure to retract the rods 142 to lowerthe weeder rods 72 to the working position. With the parallelconnections between the cylinders 136, the gauge wheels 18 will equallyshare the weight of the rear portion of the frames since, should anygauge wheel travel over a mound or the like which would place it in aposition higher than the other gauge wheels, the rod 142 of theassociated cylinder 136 would be forced inwardly forcing fluid into theother cylinders to extend their rods until the even distribution ofweight is again obtained.

According to the invention, the hydraulic system for controlling thevertical movement of the gauge wheels with respect to frames is providedwith a novel adjustable stop mechanism which prevents the exhaust offluid from the anchor ends of the cylinders after the rod 142 of one ofthe cylinders has been retracted to a predetermined position, butretains the floating characteristic of parallel connected cylinders sothat the even distribution of weight on the gauge wheels is maintained.The adjustable stop mechanism is illustrated in FIGS. 5-7 and includes avalve indicated generally at 162. The valve 162 is interposed in thefluid line 154 and is mounted on the cylinder 136b in a manner whichwill be more fully explained hereinafter. The valve 162 includes a blockportion 164 which is provide with intersecting bores 166 and 168. Thebore 166 is threaded and receives one end ofa nipple and the bore 168 isthreaded to receive a portion of the fluid line 154. The nipple 170 isretained within the bore 166 by a locknut 172, and the outer end of thenipple is internally threaded to receive a portion of the fluid line154. The inner end of the nipple 170 engages the lip of a cup-shapedmember 174 which is positioned within the inner end of the bore 166 andlimits the insertion of the nipple 170 into the bore 166. The cup-shapedmember 174 has a larger internal diameter than the nipple 170 so as toprovide an enlarged area adjacent the inner end of the hollow nipple. Aplurality. of openings 176 provided within the walls of the cup-shapedmember 174 establish fluid communication between the bore 168 and thebore of the hollow nipple.

A plunger 178 is mounted within the bore 166 for movement between aclosed position in which it extends into the hollow nipple and an openposition in which it is positioned within the enlarged area provided bythe cup-shaped member 174. The plunger 178 has a diameter of a size toslidably but snugly fit within the inner end of the hollow nipple 170.lntermediate its ends, the plunger 178 is provided with an annularrecess 180 which carries a sealing ring 182 so that when the plunger 178is moved within the inner end of the hollow nipple 170, the flow offluid through the hollow nipple is prevented. The plunger 178 isnormally biased to the enlarged area provided by the cup-shaped member174 by a compression spring 184. One end of the spring 184 extends overa spring guide 186 projecting from one end of the plunger 178 while theopposite end of the spring acts against a shoulder provided within ahollow spring guide 188. The hollow spring guide 188 is square and, asbest illustrated in FIG. 7, is provided with threaded comersso that itcan be turned into the threaded outer end of the hollow nipple 170. Aplunger stem 190 extends from the end of the plunger 178 opposite fromthe spring guide 186 and extends through a small bore 192 provided inthe valve block 164 coaxially with the bore 166.

The valve block 164 is secured in any suitable manner such as welding toa mounting bracket 194 which is shaped to conform to an outer surface ofthe cylinder l36b. The mounting bracket 194 is in turn secured to thecylinder 136b by straps 196. The plunger 178 of the valve is actuated bya push rod 198 which is mounted on the cylinder 13612 and its associatedrod 142. One end of the push rod 198 is slidably mounted within anopening provided in a mounting bracket 200 which is carried by thecylinder 136b. The mounting bracket 200 is preferably formed in anintegral part of the mounting bracket 194 for the valve 162. Theopposite end of the push rod 198 is slidably mounted within an openingprovided in a mounting bracket 202 carried by the rod 142 of thecylinder l36b. An adjustable stop member 204 is mounted on the push rod198 intermediate the mounting brackets 200 and 202, and a compressionspring 206 is mounted on the rod 198 intermediate the adjustable stop204 and the mounting bracket 202. When the rod 142 of a cylinder 136b isretracted, the mounting bracket 202 will act against the spring 206which will in turn act against the adjustable stop and move the push rod198 into engagement with the plunger stem 190 to move the plunger intothe inner end of the hollow nipple 1707 The inner end of the hollownipple 170 is tapered as at 208 to guide the plunger 178 into the nippleand movement of the plunger into the hollow nipple is limited by aninternal shoulder 210.

The operation of the above-described depth control system is as follows:The weeder rods 72 are first lowered to the desired working depth byretracting the rods 142 and rocking the frames about the wheels 16. Withthe weeder rods at the desired depth, the push rod 198 is movedforwardly into engagement with the plunger stem 190 and the stop 204 ismanually positioned so that the spring 206 is held against the mountingbracket 202. After making the one setting of the stop member 204, theweeder rod 72 can be raised and lowered to the original position withoutrequiring any attention on the part of the operator. For example, if theweeder rods 72 are to be raised to turn around at the end of a field,the operator merely needs to move the valve 152 to the right to extendthe cylinders 136. After the turn has been made, the weeder rods 72 canbe lowered by moving the valve 152 to the left to retract the cylinders136. When a cylinder 1361; has been retracted to the extent indicated bythe setting of the stop 204, the push rod 198 will contact the plungerstem 190 and push the plunger 178 into the end of the hollow nipple 170and prevent further exhaust of fluid from the anchor ends of thecylinders 136. The plunger 178 will remain within the inner end of thenipple 170 until such time as the valve 152 is again moved to the rightto supply fluid pressure from the pump 158 to the line 154 since thefluid pressure within the anchor ends of the cylinders 136 will actagainst the end of the plunger 178 to overcome he force of the spring184. It should be noted that while the exhaust of fluid through the line154 to the sump 160 is prevented, fluid is free to flow from anycylinder to any other cylinder so that one or more cylinders can beextended or retracted as long as it is accompanied by retraction orextension respectively, of one or more other cylinders. Additionalretraction of the rod 142 for the cylinder 136b does not causeadditional movement of the plunger 178 into the nipple 170, but rathermerely compresses the spring 206 between the mounting bracket 202 andthe adjustable stop 204.

While a single preferred embodiment of the invention has been describedand illustrated, various modifications obvious to those skilled in theart can be made without departing from the underlying principles of theinvention.

1 claim: 2

l. A hydraulic control system comprising: a plurality of hydraulicmotors, each of the motors including a cylinder having rod and anchorends and a rod reciprocally mounted in the cylinder and projecting fromthe rod end thereof; fluid line means connecting the anchor ends of thecylinders in parallel; additional fluid line means connected to thefirst mentioned fluid line means and being selectively connectable to asource of fluid pressure and a fluid reservoir; valve means movablebetween open and closed positions and normally biased toward the openposition interposed in the additional fluid line means; and meansresponsive to the retraction of the rod of one of the motors to apredetermined position to move the valve means to the closed position.

2. The hydraulic control system set forth in claim 1 wherein the valvemeans includes means responsive to fluid pressure within the anchor endsof cylinders when the valve means is moved to the closed position toretain the valve means in the closed position until the additional fluidline means is connected to the source of fluid pressure.

3. The control system set forth in claim 1 wherein the means to move thevalve means to the closed position includes first and second supportmembers carried by the rod and cylinder respectively of the one motor, apush rod slidably mounted on the support members for longitudinalmovement, a stop member mounted on the push rod intermediate the supportmember, and spring means encircling the push rod intermediate the firstsupport member and the stop member, and wherein the valve means ismounted on the cylinder of the one motor adjacent the end of the pushrod, whereby, upon retraction of the rod of the one motor, the springmeans will be compressed between the first support member and the stopmember and bias the push rod into engagement with the valve means tomove the valve means to the closed position.

4. A hydraulic control system comprising: a plurality of double-actingextensible and retractable hydraulic motors including cylinders havingrod and anchor ends and rods reciprocally mounted therein and extendingfrom the rod ends thereof; first fluid line means connecting the anchorends of the cylinders in parallel; second fluid line means connectingthe rod ends of the cylinders in parallel; third and fourth fluid linemeans connected respectively to the first and second fluid line meansand being connectable alternately to a source of fluid pressure and afluid reservoir whereby the rods can be extended or retracted byconnecting the third and fourth fluid lines respectively to the sourceof fluid pressure; valve means movable between open and closed positionsinterposed in one of the third and fourth fluid line means and meansresponsive to the movement of the rod of one of the motors in adirection to exhaust fluid through the one fluid line to move the valvemeans to the closed position upon the rod of the one motor reaching apredetermined position; whereby, upon the valve means being moved to theclosed position any movement of one or more of the rods must beaccompanied by movement of one or more of the rods in an oppositedirection.

5. The hydraulic control system set forth in claim 4 wherein the meansto move the valve means to the closed position is adjustable to vary theposition of the rod of the one motor at which the valve means will beclosed.

6. The hydraulic control system set forth in claim 4 wherein the valvemeans includes means responsive to fluid pressure in the one fluid linemeans to move to the open position when the one fluid line means isconnected to the source of fluid pressure.

7. A hydraulic control system comprising: a plurality of hydraulicmotors each including a cylinder having rod and anchor ends and a rodreciprocally mounted within the cylinder and projecting from the rod endthereof; first fluid line means connecting the anchor ends of thecylinders in parallel, second fluid line means connecting the rod endsof the cylinders in parallel; third and fourth fluid line meansconnected respectively to the first and second fluid line means andbeing connectable alternately to a source of fluid pressure and a fluidreservoir whereby the rods can be extended and retracted by connectingthe third and fourth fluid line means respectively to the source offluid pressure; valve means movable between open and closed positionsinterposed in the third fluid line means; the valve means includingmeans responsive to fluid pressure in the third fluid line means to movethe valve means to the open position when the third fluid line means isconnected to the source of fluid pressure; and means responsive to theretraction of the rod of one of the motors to a predetermined positionto move the valve means to the closed position whereby additionalmovement of one or more of the rods is accompanied by movement of one ormore of the other rods in an opposite direction.

8. The control system set forth in claim 7 further including meansnormally biasing the valve means toward the open position, and whereinthe valve means includes means responsive to fluid pressure in theanchor ends of the cylinders when the valve means is moved to the closedposition to retain the valve means in the closed position until thethird fluid line means is connected to the source of fluid pressure.

9. The control system set forth in claim 7 wherein the displacement ofthe rod and anchor ends of each of the cylinders is equal to thedisplacement of the rod and anchor ends respectively of the othercylinders whereby the additional movement of one or more of the rods isaccompanied by equal and opposite movement of one or more of the otherrods.

10. The control system set forth in claim 7 wherein the means responsiveto the retraction of the one of the motors includes first and secondsupport members mounted on the rod and cylinder respectively of the onemotor, a push rod slidably carried by the support members forlongitudinal movement, a stop member mounted on the push rodintermediate the support members, and means carried by the push rodbetween the first support member and the stop means and engageable bythe first support member and the stop means, whereby retractive movementof the rod of the one motor is transferred to the push rod through thefirst support member, the means carried by the push rod and the stopmember to move the push rod in a direction to move the valve means tothe closed position.

11. The control system set forth in claim 10 wherein the stop member isadjustably mounted on the push rod.

12. The control system set forth in claim 11 wherein the means carriedby the push rod and engageable by the first support member and the stopmember includes compression spring means.

13. The control system set forth in claim 12 wherein the valve meansincludes a valve body having a bore with an enlarged area near one end,a fluid passageway intersecting the enlarged area of the bore, the valvebody being interposed in the third fluid line means with the valve boreand the fluid passageway in fluid communication with the third fluidline means, a valve plunger reciprocally mounted in the valve bore andhaving a diameter substantially equal to the valve bore, means normallybiasing the plunger to the enlarged area of the bore, and a plunger stemextending from the plunger and the valve body to a position to becontacted by the push rod.

14. The control system set forth in claim 13 wherein the portion of thevalve bore leading to the enlarged area is tapered to guide the plungerwhen moving to the closed position.

15. The control system set forth in claim 14 wherein the valve bore isprovided with an inwardly directed shoulder which engages the plunger tolimit the movement of the plunger.

1. A hydraulic control system comprising: a plurality of hydraulic motors, each of the motors including a cylinder having rod and anchor ends and a rod reciprocally mounted in the cylinder and projecting from the rod end thereof; fluid line means connecting the anchor ends of the cylinders in parallel; additional fluid line means connected to the first mentioned fluid line means and being selectively connectable to a source of fluid pressure and a fluid reservoir; valve means movable between open and closed positions and normally biased toward the open position interposed in the additional fluid line means; and means responsive to the retraction of the rod of one of the motors to a predetermined position to move the valve means to the closed position.
 2. The hydraulic control system set forth in claim 1 wherein the valve means includes means responsive to fluid pressure within the anchor ends of cylinders when the valve means is moved to the closed position to retain the valve means in the closed position until the additional fluid line means is connected to the source of fluid pressure.
 3. The control system set forth in claim 1 wherein the means to move the valve means to the closed position includes first and second support members carried by the rod and cylinder respectively of the one motor, a push rod slidably mounted on the support members for longitudinal movement, a stop member mounted on the push rod intermediate the support member, and spring means encircling the push rod intermediate the first support member and the stop member, and wherein the valve means is mounted on the cylinder of the one motor adjacent the end of the push rod, whereby, upon retraction of the rod of the one motor, the spring means will be compressed between the first support member and the stop member and bias the push rod into engagement with the valve means to move the valve means to the closed position.
 4. A hydraulic control system comprising: a plurality of double-acting extensible and retractable hydraulic motors including cylinders having rod and anchor ends and rods reciprocally mounted therein and extending from the rod ends thereof; first fluid line means connecting the anchor ends of the cylinders in parallel; second fluid line means connecting the rod ends of the cylinders in parallel; third and fourth fluid line means connected respectively to the first and second fluid line means and being connectable alternately to a source of fluid pressure and a fluid reservoir whereby the rods can be extended or retracted by connecting the third and fourth fluid lines respectively to the source of fluid pressure; valve means movable between open and closed positions interposed in one of the third and fourth fluid line means and means responsive to the movement of the rod of one of the motors in a direction to exhaust fluid through the one fluid line to move the valve means to the closed position upon the rod of the one motor reaching a predetermined position; whereby, upon the valve means being moved to the closed position any movement of one or more of the rods must be accompanied by movement of one or more of the rods in an opposite direction.
 5. The hydraulic control system set forth in claim 4 wherein the means to move the valve means to the closed position is adjustable to vary the position of the rod of the one motor at which the valve means will be closed.
 6. The hydraulic control system set forth in claim 4 wherein the valve means includes means responsive to fluid pressure in the one fluid line means to move to the open position when the one fluid line means is connected to the source of fluid pressure.
 7. A hydraulic control system comprising: a plurality of hydraulic motors each including a cylinder having rod and anchor ends and a rod reciprocally mounted within the cylinder and projecting from the rod end thereof; first fluid line means connecting the anchor ends of the cylinders in parallel, second fluid line means connecting the rod ends of the cylinders in parallel; third and fourth fluid line means connected respectively to the first and second fluid line means and being connectable alternately to a source of fluid pressure and a fluid reservoir whereby the rods can be extended and retracted by connecting the third and fourth fluid line means respectively to the source of fluid pressure; valve means movable between open and closed positions interposed in the third fluid line means; the valve means including means responsive to fluid pressure in the third fluid line means to move the valve means to the open position when the third fluid line means is connected to the source of fluid pressure; and means responsive to the retraction of the rod of one of the motors to a predetermined position to move the valve means to the closed position whereby additional movement of one or more of the rods is accompanied by movement of one or more of the other rods in an opposite direction.
 8. The control system set forth in claim 7 further including means normally biasing the valve means toward the open position, and wherein the valve means includes means responsive to fluid pressure in the anchoR ends of the cylinders when the valve means is moved to the closed position to retain the valve means in the closed position until the third fluid line means is connected to the source of fluid pressure.
 9. The control system set forth in claim 7 wherein the displacement of the rod and anchor ends of each of the cylinders is equal to the displacement of the rod and anchor ends respectively of the other cylinders whereby the additional movement of one or more of the rods is accompanied by equal and opposite movement of one or more of the other rods.
 10. The control system set forth in claim 7 wherein the means responsive to the retraction of the one of the motors includes first and second support members mounted on the rod and cylinder respectively of the one motor, a push rod slidably carried by the support members for longitudinal movement, a stop member mounted on the push rod intermediate the support members, and means carried by the push rod between the first support member and the stop means and engageable by the first support member and the stop means, whereby retractive movement of the rod of the one motor is transferred to the push rod through the first support member, the means carried by the push rod and the stop member to move the push rod in a direction to move the valve means to the closed position.
 11. The control system set forth in claim 10 wherein the stop member is adjustably mounted on the push rod.
 12. The control system set forth in claim 11 wherein the means carried by the push rod and engageable by the first support member and the stop member includes compression spring means.
 13. The control system set forth in claim 12 wherein the valve means includes a valve body having a bore with an enlarged area near one end, a fluid passageway intersecting the enlarged area of the bore, the valve body being interposed in the third fluid line means with the valve bore and the fluid passageway in fluid communication with the third fluid line means, a valve plunger reciprocally mounted in the valve bore and having a diameter substantially equal to the valve bore, means normally biasing the plunger to the enlarged area of the bore, and a plunger stem extending from the plunger and the valve body to a position to be contacted by the push rod.
 14. The control system set forth in claim 13 wherein the portion of the valve bore leading to the enlarged area is tapered to guide the plunger when moving to the closed position.
 15. The control system set forth in claim 14 wherein the valve bore is provided with an inwardly directed shoulder which engages the plunger to limit the movement of the plunger. 